Question

A parallel combination of `0.1 M Omega` resistor and a `10 muF` capacitor is connected across a `1.5V` source of negligible resistance. The time required for the capacitor to get charged up to 0.75 V is approximately (in seconds).
A. `oo`
B. `log_(e) 2`
C. `log_(10)2`
D. zero

Answer 1

Correct Answer - B
b. For the capacitor to get charged up to
0.75 V, the charge on the plates should
be as follow.

`q=CE[1-e^(-t//RC)]`
or `0.75 xx 10^(-5) = 10^(-5) xx 1.5 [1-e^(-t/(10^5 xx 10^(-5)))]`
or `1/2 = [1-e^(-t)] or e^(-t) = 1/2`
Taking log on both sides, we get
`-t = -1n2 or t =0.693s`.